Because of the connection between the tap changer and the transformer winding, the voltage load on the insulation of the tap-changer depends on the maximum voltage of the transformer, the regulating range, the pressure regulating position, the voltage regulating mode, the winding connection method and the winding structure arrangement, etc.

The insulation of the tap switch is divided into external insulation and inner insulation.

The withstand voltage of external insulation has been standardized and incorporated into GB and IEC standards. In Single-Phase and three-phase Y-Joint switches, the external insulation is the ground insulation. On the D-connected three-phase tap switch, the outer insulation is the ground insulation and interphase insulation, both of which are determined by the highest voltage of the equipment um. The total wave impact of the external insulation is proportional to the test voltage of the power frequency, which is related to Um, between 2.5 (um=72.5kv, full wave impulse voltage value 350kv/AC power frequency Voltage value 140kV) and 2.26 (um=420kv, full wave impulse voltage value 1 425kv/AC power frequency Voltage value 630kV). Therefore, the external insulation is obviously determined by the frequency-voltage test, and the impact test has little effect on the tap-changer.

The internal insulation of the tap switch cannot be standardized and can only be calibrated to the rated withstand voltage. It is based on the experience of voltage load in the transformer test, and then according to the actual need to be divided into several grades.